I was surprised how much I enjoyed Avatar: The Last Airbender. The second Avatar series was also quite good in its own way, but the first series holds a special place for me.
What to watch depends on what you like. Try http://myanimelist.net/
for reviews and recommendations, pick a show and try it. If you don't like it, try something else. You'll find something you like pretty quick. One tip, though: Original Japanese voice with subtitles is almost always better than dubbed. Sometimes it's because the Japanese voice actors are serious professionals (which is usually true), but even if that weren't the case, most of the time the English dubbing is just horribly done. Trying to watch dubbed versions of shows after watching the original with subtitles is unbearable, IMO. There are only a very few exceptions, in my experience. One of those is the movie Akira, where both versions are good for different reasons. Kaneda is just much cooler sounding in the dub, but the original is a bit more authentic to the story/dialogue.